A result from a routine blood test can raise questions when a value falls outside the typical range. One such measurement is the Red Blood Cell Distribution Width (RDW), a standard component of a Complete Blood Count (CBC). A CBC provides a broad overview of the cells circulating in the blood, including red cells, white cells, and platelets.
The RDW measures the variation in the size and volume of your red blood cells, which are responsible for carrying oxygen from your lungs to the rest of the body. Healthy red blood cells are uniform in size, and the RDW test quantifies this variation as a percentage.
Understanding an RDW of 15.7
To understand a specific RDW value, it’s necessary to know the standard reference range. While ranges can vary slightly between laboratories, a normal RDW is between 11.5% and 15%. An RDW level of 15.7% is considered elevated because it falls above this upper limit, indicating more variation in red blood cell size than is expected.
This increased variation in red blood cell size is medically termed anisocytosis. When the bone marrow produces red blood cells of unequal sizes, the RDW value on a blood test will be high. This finding suggests something may be affecting the normal production or lifespan of these cells, which requires investigation into potential underlying causes.
Potential Causes of Elevated RDW
A high RDW is frequently associated with nutritional deficiencies that disrupt red blood cell production, such as shortages of iron, vitamin B12, or folate. Iron is a component of hemoglobin, the protein in red blood cells that binds to oxygen. An iron deficiency can lead to the production of smaller red blood cells, and the mix with normal-sized cells increases size variation, raising the RDW.
Similarly, vitamin B12 and folate are necessary for red blood cell maturation. A deficiency in either vitamin can cause the production of unusually large red blood cells, a condition known as macrocytic anemia. The presence of these large cells alongside normal ones also leads to a higher RDW.
Beyond nutrient deficiencies, other conditions can contribute to an elevated RDW. Chronic liver disease or certain inherited blood disorders, such as some forms of thalassemia, can affect red blood cell production and survival, leading to increased size variation. Another possibility is a recent blood transfusion, as the introduction of donor blood cells can create a temporary mix of cell populations of different sizes.
How RDW is Used in Diagnosis
An RDW result of 15.7 is not a diagnosis in itself. Healthcare providers interpret the RDW in the context of other blood test results, particularly the Mean Corpuscular Volume (MCV), which measures the average size of your red blood cells. Looking at both the RDW and MCV together helps narrow down the possible causes of an abnormality.
The combination of these two values helps classify different types of anemia. For instance, a high RDW paired with a low MCV (smaller than average cells) suggests iron deficiency anemia. Conversely, a high RDW combined with a high MCV (larger than average cells) points toward a deficiency in vitamin B12 or folate.
In some cases, the RDW might be high while the MCV is normal. This pattern can indicate an early stage of a nutrient deficiency, where the average cell size has not yet shifted, but the bone marrow has begun producing cells of varying sizes. It could also point to other conditions, like certain hemoglobinopathies or chronic liver disease.
Next Steps and Management
Receiving an RDW result of 15.7 means the next step is to discuss the findings with the healthcare provider who ordered the test. They will interpret this value within the full context of your health, including your symptoms, medical history, and the other results from the complete blood count.
A doctor will determine the appropriate course of action based on a full evaluation. If a nutritional deficiency is suspected, management might involve dietary changes to include more iron-rich foods or foods high in B vitamins. Supplementation with iron pills or vitamin B12 injections may also be recommended to correct the deficiency.
Your provider may also decide that further testing is needed to pinpoint the cause of the elevated RDW. This could involve more specific blood tests to check iron, vitamin B12, and folate levels directly or to investigate other potential underlying conditions. Management is tailored to the individual and the root cause of the abnormal finding.